This invention relates to an automatic electric switch assembly with associated timers for re-synchronizing a time clock with real time after a power interruption.
Electric power companies are searching for methods to reduce their peak demands. Special rates and demand charges have been devised to encourage large commercial and industrial accounts to reduce their demand during peak periods. However, the bulk of the load (the residential customer) represents a special problem.
Each individual customer returns a very small amount of money to the utility. Any plan to encourage the residential customer to reduce peak demand must have a low first cost to make a reasonable return on the investment. Such concepts as demand metering are very unpopular as they represent an additional cost to the customer.
The only practical means available to power companies for reducing residential demand is to "turn off" the water heater during peak periods. The water heater is an energy storage device that can supply hot water after being "turned off".
Controlling a residential water heater during peak periods will reduce the peak demand per residence a minimum of 1 KW. This reduction would return a power company $5.70/month, for example, in the winter and $2.48/month in the summer, based on the wholesale power rate charged utilities by a typical power company.
______________________________________ 1984 Bonneville (Oregon) Power Administration (B.P.A.) Rate Schedule CONSUMPTION SEASON CHARGE DEMAND CHARGE ______________________________________ WINTER 1.67./KWH $5.70/KW SUMMER 1.34./KWH $2.48/KW ______________________________________
Devices are on the market to turn off water heaters during peak periods. However, their initial cost discourages their purchase. The most common form is a watthour meter with a built in time clock that operates a power relay at the water heater. The cost of the meter is $150 and the relay is $30. The installation cost is $75.
The cheapest means of controlling a water heater is through the standard (interval) timer employing mechanical trippers and a synchronous (clock) motor. However it cannot maintain correct time continuously due to power outages. This problem makes the standard interval timer almost useless to utilities.
The present invention overcomes this objection and makes the use of the timer feasible for utilities. The first cost of a timer with this enhancement is estimated at $28-$34. Installation cost is $20. The timer thus would pay back its initial investment in one year.
It accordingly is the general object of this invention to provide a simple and economical means to automatically "reset" or synchronize a time clock after one or more power outages.
Another object of this invention is to provide a compact synchronizing device which can be placed inside the cabinet of most time clocks.
A further object of this invention is to provide an electric time clock synchronizing device having very low power requirements and consequently requiring a very small battery as a power source.
These and other objects of the invention are achieved by the provision of an automatic electric time delay switch assembly for maintaining a time switch clock synchronized with real time in the event of an electric power failure which comprises an electric circuit including a power source and a time switch clock.
First electronic time delay means in the electric circuit is operative to measure a first predetermined period of time after the occurrence of a power failure. Electric relay means in the electric circuit is operative in the open condition to disconnect the clock from the power source if the power failure remains at the conclusion of the said first predetermined time period.
Second electronic time delay means in the electric circuit is operative upon disconnection of the clock from the power source to maintain the relay means in its open condition for a second predetermined period of time which corresponds to a complete cycle of the clock. The second electronic time delay means then is further operative to re-connect the clock to the power source in synchronization with real time at the conclusion of the second predetermined period of time if, during that period, power has been restored to the circuit.